Such a pipe coupling is known from FR-A-2.072.296 (corresponding to U.S. Pat. No. 3,712,647), showing a sealing ring having a sealing sheath which encloses the helical core annulus both in circumferential and cross section direction. More particularly, it shows a construction with which the sealing sheath does not completely enclose the core annulus, so that a circular slit is formed on one axial end of the ring.
It has now been found that the construction in which the core annulus is completely enclosed by the sealing sheath also in the cross section plane, is particularly suitable for use in conjunction with a sleeve, which is designed to accomodate and interconnect pipes of various diameters. This construction is more particularly suitable for bridging the differences in outer diameter occurring with pipes of the same nominal diameter (i.e: inner diameter) but formed of different material. It is considered that with a sealing ring having such a sealing sheath, in contrast to an embodiment having a slit on on axial end of the ring, it is easier to tangentially compress the ring in a uniform manner.
Based on this insight, it is the aim of the present invention to provide an improved sleeve portion so as to take maximum advantage of the wide limits of use of the selected sealing ring, while keeping the cross sectional diameter of the sealing ring relatively small (which means a relatively thin sealing ring).